1'Adg'.3  in 


O.  E.  S.  Library,  So*.  2. 


r  o  n  N 

•S 
no,  1 1? 


THE 


lent  Agricultural  Experiment  S 

NEW    HAVEN,     CONN. 


BULLETIN     I> To.     1 1 


Office  of 

trnwi  smiais. 


Rec'd 


94  02  06 


,AnswU94090< 


JANUARY,    1894 


CONTENTS. 

(Notice  as  to  Bulletins,  page  2). 

THE  BABCOCK  METHOD  OF   DETERMINING  FAT  IN   MILK 

AND   MILK  PRODUCTS. 


Weight  of  the  Milk, 

Directions  for  Sampling,  Whole  milk  of  single  cows, 

of  a  herd, 
Skim  milk  and  Butter  milk, 
Cream, 
Preservation  of  Samples  to  be  subsequently  tested, 
Description  of  Apparatus,  Test  Bottles, 
Pipettes, 
Acid  Measure, 
Centrifugal  Machine, 
Oil  of  Vitriol, 
The  Operation  of  Testing,  .... 

Measuring  the  Milk, 
Adding  the  Acid, 
Whirling  the  Bottles, 
Filling  the  Bottles  with  Hot  Water, 
Measuring  the  Fat, 


Page 
3 
4 
4 
5 
5 
5 
5 
7 
7 
7 
7 
7 


Notice  as  to  Bulletins. 

The  Bulletins  of  this  Station,  usually  issued  quarterly  or 
oftener,  are  mailed  free  to  citizens  of  Connecticut  who  apply  for 
them,  and  to  others,  as  far  as  the  limited  editions  permit. 

Applications  should  be  renewed  annually  before  January  1st. 

The  matter  of  all  the  Bulletins  of  this  Station  in  so  far  as  it 
is  new  and  of  permanent  value  will  be  made  part  of  the  Annual 
Report  of  the  Director. 

Bulletins  earlier  than  No.  71  and  Nos.  83,  93,  100,  101,  102, 
109  and  111  are  exhausted  and  cannot  be  supplied. 


Notice  as  to  Supply  of  Station  Reports. 

The  Station  has  no  supply  of  its  Annual  Reports  for  the  years 
1877,  1878,  1879,  1880,  1881,  1883,  1887,  and  1891. 

The  Annual  Report  of  this  Station,  printed  at  State  expense,  is 
by  law  limited  to  an  addition  of  12,000  copies,  of  which  5,000 
copies  are  bound  with  the  Annual  Report  of  the  Connecticut 
State  Board  of  Agriculture,  and  distributed  by  the  Secretary  of 
the  Board,  T.  S.  Gold,  West  Cornwall,  Conn. 

After  exchanging  with  other  Experiment  Stations  and  Agricul- 
tural Journals,  the  Reports  remaining  at  the  disposal  of  the  Sta- 
tion will  be  sent  to  citizens  of  Connecticut  who  shall  seasonably 
apply  for  them,  and  to  others  as  long  as  the  supply  lasts. 


THE  BABCOCK  METHOD. 


THE  BABCOCK  METHOD  OF  DETERMINING  THE 

PROPORTION  OF  FAT  IN  MILK  AND 

MILK  PRODUCTS. 

This  method  is  based  on  the  fact  that  when  milk  is  mixed  in 
proper  proportions  with  sulphuric  acid  of  a  certain  strength 
the  acid  dissolves  or  mixes  with  all  the  milk-ingredients  except 
the  butter-fat.  Then  with  suitable  apparatus  the  butter-fat  is 
completely  brought  to  the  surface  and  accurately  measured. 

The  quantity  of  butter-fat  shown  by  the  Babcock  method,  is 
now  the  basis  of  payment  for  milk  or  cream  in  many  of  the  most 
successful  creameries  east  and  west.  The  use  of  this  method, 
which  is  unquestionably  more  satisfactory  than  any  other  now 
known  that  can  be  used  on  the  farm  or  in  the  creamery,  is  rapidly 
increasing  and  promises  to  become  almost  universal. 

In  Bulletin  106  of  this  Station,  issued  in  1891,  the  attention  of 
Connecticut  dairymen  was  called  to  the  method.  The  supply  of 
that  Bulletin  has,  however,  long  been  exhausted.  To  answer 
inquiries  more  frequently  made  of  late  regarding  the  way  to  work 
the  Babcock  test,  is  the  object  of  this  Bulletin.  In  its  prepara- 
tion full  use  has  been  made  of  Bulletin  36,  of  the  Wisconsin 
Experiment  Statiou,  written  by  Dr.  Babcock. 

Directions  are  first  given  for  sampling  milk  and  its  products. 
Then  follow  instructions  for  preserving  samples  which  cannot  be 
immediately  tested,  and  lastly  the  method  of  executing  the  tests 
is  fully  described. 


WEIGHT   OF  THE   MILK. 

To  determine  the  quantity  of  buttei--fat  which  a  cow  daily  pro- 
duces it  is  absolutely  necessary  in  the  first  place  to  know  the 
quantity  of  milk  which  she  gives. 

Weigh  the  milk  accurately  at  milking  time,  which  may  be  con- 
veniently done  on  a  spring  balance  in  a  pail  which  weighs  an 
even  number  of  pounds.*     If  the  milk  cannot  be  weighed,  the 

*  The  pail  may  be  brought  to  the  required  weight  by  solderiug  the  necessary 
amount  of  lead  on  the  outside. 


4  CONNECTICUT   AGRICULTURAL    STATION,    BULL.    11.7. 

number  of  quarts  multiplied  by  2.15  will  give  its  approximate 
weight.  Thus:  8£  quarts  is  pretty  nearly  (8£  X  2.15)  =  18.3 
pounds. 

The  measuring  must  be  accurate.  Froth  is  not  milk.  A  quart 
measure  filled  to  a  quarter  of  an  inch  of  the  top  is  not  a  quart. 
An  "eight  quart"  pail  sometimes  holds  considerably  less  or 
more  than  eight  quarts. 


Directions  for  Sampling  Whole  Milk. 

Milk  of  Single  Cows. — Milk  that  has  soured  or  on  which  cream 
has  risen  and  dried,  so  as  to  form  a  clot  or  skin,  cannot  be  accu- 
rately sampled  on  the  farm. 

Thoroughly  mix  the  milk,  as  soon  after  milking  as  possible, 
either  by  pouring  three  or  four  times  from  one  pail  to  another,  or 
by  stirring  vigorously  with  a  dipper.  To  secure  an  accurate 
sample,  thorough  mixing  is  absolutely  essential.  Failure  to 
secure  a  fair  sample  makes  the  test  worthless  or  worse  than 
worthless.  Immediately  after  mixing,  dip  out  a  sample  of  about 
one  half  gill  or  two  ounces.  From  this  a  sample  may  be  at  once 
measured  in  the  way  to  be  described  later  for  testing,  or  the 
whole  quantity  may  be  put  into  a  clean  and  dry  bottle,*  with  a 
preservative  when  necessary,  and  kept  till  used  in  a  cold  place 
where  it  will  not  freeze. 

Mixed  Milk  of  a  Herd. — Into  some  vessel  like  a  cream  carrier, 
pour  all  the  milk  from  the  pails  or  cans  at  one  time,  and  from 
such  a  height  that  the  whole  quantity  is  stirred  up  from  the 
bottom.  Then  with  a  cup,  dipper  or  pitcher,  at  once  take  out 
about  a  pint.  Stir  this  thoroughly  with  a  spoon  immediately 
before  pouring  into  the  sample  bottle,  or  before  measuring  the 
quantity  for  the  Babcock  test.  If  there  is  no  can  at  hand  large 
enough  to  hold  the  whole  lot  of  milk,  very  accurate  samp- 
ling is  not  possible.  Still  if  the  milk  is  in  a  number  of  cans  or 
pails  of  the  same  size  or  shape,  and  all  have  the  same  quantity  of 
milk  in  them,  a  pretty  fair  sample  may  be  got  by  taking  the 
same  quantity  of  milk,  a  gill,  pint  or  quart,  from  each  can  or  pail, 
after  thorough  stirring  as  already  described,  mixing  these  samples 
thoroughly,  and  then  taking  a  single  sample  from  the  mixture. 

*  Rather  than  try  to  use  large  bottles  or  those  not  perfectly  clean  it  is  better  to 
buy  from  a  druggist  new  two-ounce  bottles  with  new  corks. 


APPAEATUS.         •  O 

Skim-Milk  and  Butter-Milk.- — The  same  course  should  be 
followed  as  with  the  mixed  milk  of  a  herd.  The  whole  quantity 
of  the  skim-milk  or  butter-milk  should  be  mixed.  *  The  sample 
must  not  be  taken  from  a  part  of  it.  If  possible  weigh  the  skim- 
milk  or  the  butter-milk.  Then  from  this  weight  and  the  per 
cent,  of  fat  the  whole  loss  of  butter-fat  can  be  calculated. 

Cream. — Cream  that  is  very  thick,  clotted  or  soured  cannot 
readily  be  sampled  on  the  farm.  The  same  is  true  of  centrifugal 
cream  when  it  is  badly  frothed ;  but  sweet  cream  thin  enough  to 
pour  freely,  may  be  sampled  in  the  same  way  as  whole  milk,  after 
pouring  it  two  or  three  times  from  one  vessel  to  another. 


PRESERVATION   OF   SAMPLES   TO   BE   SUBSE- 
QUENTLY TESTED. 

Potassium  bichromate  will  keep  milk  from  souring,  and  in  prop- 
er condition  for  testing  for  some  time.  Although  poisonous,  it 
is  by  no  means  so  violent  a  poison  as  corrosive  sublimate,  which 
some  have  recommended,  and  may  be  used  with  comparatively  little 
danger.  It  gives  to  milk  an  orange  yellow  color  easily  distin- 
guishable from  pure  milk,  which  lessens  the  clanger  from  its  use. 
Packages  containing  this  material  and  samples  of  milk  preserved 
by  it  should,  however,  always  be  labelled  "  Poison."  To  every 
half  gill  (2  ounces)  of  milk  add  about  one  grain  of  powdered 
potassium  bichromate  and  shake  the  bottle  till  it  is  dissolved  and 
evenly  mixed.  The  quantity  used  need  not  be  weighed  as  the 
amount  may  vary  considerably  without  affecting  the  results.  As 
much  of  the  pulverized  bichromate  as  equals  a  buckshot  in  bulk 
will  suffice.     Keep  the  samples  in  a  cool  place  if  possible. 

Apparatus   for   the   Babcock   Method. 

Test  Bottles. — The  test  bottles  used  for  whole  milk  (figure  1) 
have  graduations  from  0  to  10,  each  division  of  the  scale  repre- 
senting 0.2  per  cent.  These  bottles  can  be  used  also  for  skim- 
milk  and  butter-milk,  but  a  bottle  which  holds  twice  as  much  and 
has  a  scale  graduated  to  0.1  per  cent,  (shown  in  figure  2)  admits 
of  more  accurate  work  with  skim-milk  or  butter-milk. 

Of  the  several  bottles  which  have  been  recommended  for  test- 
ing cream,  we  prefer  for  practical  dairy  work,  one  devised  at  this 
Station.     It  has  a  neck  of   wider  bore  than   the  milk  bottles, 


6  CONNECTICUT   AGRICULTURAL    STATION,    BULL.    117. 


\~r 


__i0 

§-a 

=-6 
!E_3 


Mar.  l. 


Whole  Milk 
Bottle. 


Y7 

3 


\ 


Fig.  2. 

Skim  Milk 
Bottle. 


Fig.  3. 

Cream 
Bottle. 


A 


17.6  c.c. 


I7.5cc. 


VI 

Fig.  4. 

Pipette 
for  Milk. 


2 


k 


Fig.  5. 

Acid 
Measure. 


graduated  from  0  to  30  (figure  3).  The  graduated  portion  of  the 
neck  is  about  the  same  length  as  that  of  the  whole  milk  bottles, 
but  has  three  times  its  capacity.  The  divisions  of  the  scale  rep- 
resent 0.5  per  cent.,  but  can  be  read  to  a  quarter  of  a  division. 


MAKING  THE    TEST.  7 

Owing  to  the  lower  specific  gravity  of  cream,  18  cubic  centi- 
meters of  it  are  used  instead  of  17.6  c.c,  as  in  the  case  of  milk. 

Pipettes. — For  whole  milk,  skim-milk  and  butter-milk  a  pipette 
delivering  17.6  cubic  centimeters  is  used  (figure  4).  When  skim- 
milk  and  butter-milk  are  tested  in  bottle  No.  2,  the  pipette  is 
filled  twice,  that  is  to  say  35.2  c.c.  are  used  for  the  test.  An  18 
c.c.  pipette  must  be  used  with  the  cream  bottle. 

Acid  Measure. — This  is  a  glass  graduate  which  holds,  when 
filled  to  the  mark,  17.5  c.c.     See  fig.  5. 

Centrifugal  Machine. — There  are  machines  of  various  patterns 
put  on  the  market  by  manufacturers  of  dairy  supplies,  all  of 
which  are  suitable  for  the  purpose.  The  sizes  vary  from  four 
bottle  testers  to  those  carrying  fifty  or  more  bottles,  the  larger 
being  designed  for  factory  use.  The  wheel  to  whose  circum- 
ference the  bottles  are  attached  should  make  from  700  to  1200 
revolutions  per  minute  according  to  its  diameter,  about  *700  revo- 
lutions being  sufficient  for  the  larger  Avheels  with  a  diameter  of 
about  20  inches,  while  small  12-inch  wheels  should  run  at  the  rate 
of  about  1200  revolutions  per  minute. 

Commercial  Sulphuric  Acid  (Oil  of  Vitriol).  —  This  should 
have  a  specific  gravity  of  1.82.  If  much  stronger,  the  fat  will 
be  of  a  dark  color;  if  weaker  it  will  be  contaminated  with  undis- 
solved curd.  The  acid  should  be  kept  in  tightly  stoppered  bot- 
tles, as  otherwise  it  rapidly  absorbs  moisture  from  the  air  and 
becomes  too  weak.  The  stopper  should  be  of  either  glass  or 
rubber,  and  not  of  cork  which  is  rapidly  destroyed  by  the  acid. 
This  oil  of  vitriol  is  extremely  corrosive.  It  will  ruin  very 
quickly  clothing  or  leather  on  which  it  falls,  and  soon  makes 
painful  burns  if  in  contact  with  the  skin.  If  the  hands  come  in 
contact  with  it  they  should  be  immediately  and  thoroughly 
rinsed.     The  greatest  care  must  be  used  in  handling  it. 

MAKING  THE   TEST. 

The  details  of  the  process  of  testing  are  the  same  for  whole 
milk,  skim-milk,  butter-milk  and  cream  (except  as  far  as  the 
quantities  for  testing,  and  the  form  of  the  bottles  is  concerned) 
and  are  best  described  substantially  in  Dr.  Babcock's  own  words 
as  follows  : 


8  CONNECTICUT   AGRICULTURAL   STATION,    BULL.    117. 

Measuring  the  Milk, — The  pipette  is  filled  by  placing  its  lower  end  in  the  milk 
and  sucking  at  the  upper  end  until  the  milk  rises  above  the  mark  on  the  stem ; 
then  remove  the  pipette  from  the  mouth  and  quickly  close  the  tube  at  the  upper 
end  by  firmly  pressing  the  end  of  the  fore-finger  upon  it  to  prevent  access  of  air. 
So  long  as  this  is  done  the  milk  cannot  flow  from  the  pipette.  Holding  the  pi- 
pette in  a  perpendicular  position,  with  the  mark  on  a  level  with  the  eye.  carefully 
relieve  the  pressure  on  the  finger  so  as  to  admit  air  slowly  to  the  space  above  the 
milk.  In  order  to  more  easily  control  the  access  of  air  both  the  finger  and  end 
of  the  pipette  should  be  dry.  When  the  upper  surface  of  the  milk  coincides  with 
the  mark  upon  the  stem,  the  pressure  should  be  again  applied  to  stop  the  flow  of 
milk.  Next,  place  the  point  of  the  pipette  in  the  mouth  of  one  of  the  test  bot- 
tles, held  in  a  slightly  inclined  position  so  that  the  milk  will  flow  down  the  side 
of  the  tube  leaving  a  space  for  the  air  to  escape  without  clogging  the  neck,  and 
remove  the  finger  allowing  the  milk  to  flow  into  the  bottle.  After  waiting  a 
short  time  for  the  pipette  to  drain,  blow  into  the  upper  end  to  expel  the  milk 
held  by  capillary  attraction  in  the  point.  If  the  pipette  is  not  dry  when  used  it 
should  be  filled  with  the  milk  to  be  tested,  and  this  thrown  away  before  taking 
the  test  sample.  If  several  samples  of  the  same  milk  are  taken  for  comparison, 
the  milk  should  be  poured  once  from  one  vessel  to  another  after  each  sample  is 
measured.  Neglect  of  this  precaution  may  make  a  perceptible  difference  in  the 
results,  through  the  separation  of  cream,  especially  when  the  milk  examined  is 
rich. 

Persons  who  have  had  no  experience  in  the  use  of  the  pipette  will  do  well  to 
practice  a  short  time  by  measuring  water  into  a  test  bottle  before  attempting  to 
make  an  analysis. 

Of  skim-milk  or  butter-milk  take  double  the  quantity  (filling  the  pipette  twice) 
and  use  the  skim-milk  test  bottle  (fig.  2). 

"With  cream  use  the  18  cubic  centimeter  pipette  and  the  cream  test  bottle, 
(fig.  3).     The  further  proceeding  is  the  same  in  all  cases. 

Adding  the  Acid. — After  the  milk  has  been  measured  into  the  test  bottle  the 
test  may  be  proceeded  with  immediately,  or  the  bottles  may  be  left  for  a  day  or 
two  without  materially  changing  the  results;  samples  that  have  remained  in  the 
test  bottles  two  or  three  weeks  and  which  had  commenced  to  mould  before  the 
acid  was  added,  have  given  the  same  amount  of  fat  as  samples  tested  immediately 
after  being  measured.  If  the  milk  has  become  coagulated,  the  curd  should  be 
broken  up  by  shaking  the  test  bottle  before  the  acid  is  added.  It  is  advisable, 
however,  that  the  test  be  proceeded  with  immediately  after  the  samples  are 
measured,  if  possible. 

The  volume  of  commercial  sulphuric  acid  required  for  a  test  is  approximately 
the  same  as  that  of  the  milk,  or  17.5  c.  c.  for  the  ordinary  test.  If  too  little  acid 
is  added,  the  casein  is  not,  all  held  in  solution  throughout  the  test,  and  an  imper- 
fect separation  of  the  fat  results.  If  too  much  acid  is  used,  the  fat  itself  is 
attacked.  The  acid  need  not  be  measured  with  great  accuracy,  as  small  varia- 
tions will  not  affect  the  result. 

Great  care  must  be  taken  in  handling  the  acid  to  avoid  getting  any  of  it  upon 
the  skin  or  clothing,  as  it  is  very  corrosive.  If  by  accident  any  is  spilled  upon 
the  hands  or  clothes,  it  should  be  washed  off  immediately,  using  plenty  of  water. 
A  prompt  application  of  ammonia  water  to  clothing  upon  which  acid  is  spilled 
may  prevent  the  destruction  of  the  fabric,  and  restore  the  color. 


MAKING   THE    TEST.  9 

When  all  of  the  samples  of  milk  to  be  tested  are  measured  ready  for  the  test, 
the  acid  measure  is  filled  to  the  17.5  c.  c.  mark  with  sulphuric  acid,  and  from  this 
it  is  carefully  poured  into  a  test  bottle,  containing  milk,  that  is  held  in  a  slightly 
inclined  position  for  reasons  given  in  directions  for  measuring  the  milk/  The 
acid  being  much  heavier  than  milk  sinks  directly  to  the  bottom  of  the  test  bottle 
without  mixing  with  the  milk  that  floats  upon  it.  The  acid  and  milk  should  be 
thoroughly  mixed  together  by  gently  shaking  with  a  rotary  motion.  At  first 
there  is  a  precipitation  of  curd  from  the  milk,  but  this  rapidly  dissolves.  There 
is  a  large  amount  of  heat  evolved  by  the  chemical  action,  and  the  solution,  at 
first  nearly  colorless,  soon  changes  to  a  very  dark  brown,  owing  to  the  charring 
of  the  milk  sugar  and  perhaps  some  other  constituents  of  the  milk. 

Whirling  the  Bottles. — The  test  bottles  containing  the  mixture  of  milk  and  acid 
should  be  placed  in  the  machine  and  whirled  directly  after  the  acid  is  added. 
An  even  number  of  bottles  should  be  whirled  at  the  same  time,  and  they  should 
be  placed  in  the  wheel  in  pairs  opposite  to  each  other,  so  thai  the  equilibrium  of 
the  apparatus  will  not  be  disturbed.  When  all  of  the  test  bottles  are  placed  in 
the  apparatus,  the  cover  is  placed  upon  the  jacket,  and  the  machine  turned  at  the 
proper  speed  for  about  five  minutes.  The  test  should  never  be  made  without  the 
cover  being  placed  upon  the  jacket  as  this  not  only  prevents  the  cooling  of  the 
bottles  when  they  are  whirled,  but  in  case  of  the  breakage  of  bottles  may  protect 
the  face  and  eyes  of  the  operator  from  injury  by  pieces  of  glass  or  hot  acid.  The 
machine  should  be  frequently  examined  to  make  certain  that  there  is  no  slipping 
of  belts  or  frictional  bearings  which  may  cause  too  slow  motion  and  result  in  an 
imperfect  separation  of  the  fat.  Managed  in  this  way  no  extra  heat  is  required, 
as  that  caused  by  the  chemical  action  is  sufficient  to  keep  the  fat  liquid.  If  the 
bottles  have  stood,  after  the  acid  is  added,  until  the  contents  are  cooled  below 
100°  F.,  they  should  be  warmed  to  about  200°  F.  by  placing  them  in  hot  water, 
before  whirling. 

Filling  the  bottles  with  hot  water. — As  soon  as  the  bottles  have  been  sufficiently 
whirled,  they  should  be  filled  to  about  the  seven  per  cent,  mark,  with  hot  water. 
If  practicable,  distilled  or  rain  water  should  be  used  for  the  purpose.  The  bottles 
are  most  conveniently  filled  by  placiug  a  vessel  containing  boiling  water  above 
the  machine,  and  by  means  of  a  syphon  made  from  a  small  rubber  tube  with  a  glass 
tip,  run  the  water  directly  into  the  bottles  without  removing  them  from  the 
wheel.  The  flow  of  water  can  be  perfectly  controlled  by  a  pinch  cock  upon  the 
rubber  tube.  If  only  a  few  tests  are  to  be  made,  the  bottles  may  be  easily  filled 
with  a  pipette,  or  by  pouring  from  a  graduate.  The  cover  should  then  be  replaced 
and  the  machine  turned  for  about  one  minute,  after  which  the  fat  should  be 
measured. 

If,  when  managed  in  this  way,  clots  of  curd  or  other  matter  are  mingled  with 
the  fat,  making  the  reading  uncertain,  the  difficulty  can  usually  be  avoided  by 
adding  the  hot  water  in  two  portions,  filling  the  bottle  at  first  only  to  the  neck 
and  after  whirling  for  about  one  minute  adding  sufficient  hot  water  to  bring  the 
fat  into  the  graduated  neck,  after  which  the  bottle  should  be  whirled  and  the  fat 
measured. 

Measuring  the  fat. — The  fat  when  measured  should  be  warm  enough  to  flow 
readily,  so  that  the  line  between  the  acid  liquid  and  the  column  of  fat  will  quickly 
assume   a   horizontal   position   when   the   bottle   is   removed  from  the  machine. 


Fig.  6. 


10  CONNECTICUT    AGRICULTURAL   STATION,    BULL.    117. 

Any  temperature  between  110°  F.  and  150°  F.  will  answer,  but  the  higher 
temperature  is  to  be  preferred.  The  slight  difference  in 
the  volume  of  fat  due  to  this  difference  in  temperature  is 
not  sufficient  to  materially  affect  results. 

To  measure  the  fat,  take  a  bottle  from  its  socket, 
and  holding  it  in  a  perpendicular  position  with  the  scale 
on  a  level  with  the  eye,  observe  the  divisions  which 
-<f  mark  the  highest  and  the  lowest  limits  of  the  fat. 
The  difference  between  these  gives  the  per  cent,  .of  fat 
directly.  The  reading  can  easily  be  taken  to  half  divis- 
ions or  to  one-tenth  per  cent. 

The  line  of  division  between  the  fat  and  the  liquid 
beneath  is  nearly  a  straight  line  and  no  doubt  need  arise 
concerning  the  reading  at  this  point  but  the  upper 
surface  of  the  fat  being  concave  errors  often  occur  by 
reading  from  the  wrong  place.  The  reading  should  be 
taken  at  the  line  where  the  upper  surface  of  the  fat 
meets  the  side  of  the  tube  and  not  from  surface  of  fat 
in  the  center  of  the  tube  nor  from  the  bottom  of  the 
dark  line  caused  by  the  refraction  of  the  curved  surface. 
For  instance  in  Fig.  6  the  reading  should  be  taken  from 
a  to  b  and  not  to  c  or  d. 
The  reading  may  be  made  with  less  liability  of  error  by  measuring  the  length 
of  the  column  of  fat  with  a  pair  of  dividers,  one  point  of  which  is  placed  at  the 
bottom  and  the  other  at  the  upper  limit  of  the  fat.  The  dividers  are  then 
removed  and  one  point  being  placed  at  the  0  mark  of  the  scale  on  the  bottle  used, 
the  other  will  be  at  the  per  cent,  of  fat  in  the  milk  examined. 

Sometimes  bubbles  of  air  collect  at  the  upper  surface  of  the  column  of  fat  and 
prevent  a  close  reading ;  in  such  cases  a  few  drops  of  strong  alcohol  (over  90  per 
cent.)  put  into  the  tube  on  top  of  the  column  of  fat,  will  cause  the  bubbles  to  dis- 
appear and  give  a  sharp  line  between  the  fat  and  alcohol  for  the  reading.  When- 
ever alcohol  is  used  for  this  purpose,  the  reading  should  be  taken  directly  after 
the  alcohol  is  added,  as  after  it  has  stood  for  a  time,  the  alcohol  partially  unites 
with  the  fat  and  increases  its  volume. 

Whenever  the  fat  is  not  quite  clear,  more  satisfactory  results  may  be  obtained 
by  allowing  the  bottles  to  stand  until  the  fat  has  crystallized  and  the  nwarm  them 
by  placing  the  bottles  in  hot  water,  before  taking  the  reading. 

If  the  column  of  fat  is  less  than  about  one  division  as  will  often  happen  with 
skim-milk,  butter-milk  or  whey,  it  may  assume  a  globular  form  instead  of  a  uni- 
form layer  across  the  tube ;  when  this  occurs  the  fat  can  usually  be  estimated 
with  sufficient  accuracy  by  simple  inspection,  but  in  such  cases  it  is  better  to  take 
a  double  portion  of  milk  in  a  large  bottle. 


The  way  of  reading  is  illustrated  in  the  figure.  The  bottom  of 
the  clear  yellow  liquid  fat  layer  is  at  a.  The  upper  surface  is 
represented  by  b,  c,  d.  The  readings  are  1.4  and  o.T.  The  dif- 
ference, 4.3,  is  the  per  cent,  of  fat  in  this  sample  of  milk. 


MAKING   THE   TEST. 


11 


To  the  breeder  of  dairy  stock,  to  the  dairyman  who  wishes  to 
keep  only  cows  that  it  will  pay  him  to  keep,  and  to  creameries, 
whether  milk  gathering  or  cream  gathering,  the  Babcock  tester 
can  be  of  the  greatest  service. 

It  is  beyond  the  purpose  of  the  present  Bulletin  to  discuss  this 
part  of  the  subject. 

This  Station  is  ready  to  cooperate  with  any  creamery  or  dairy- 
man, wishing  further  information  or  practical  experience  in  work- 
ing the  method,  and  when  necessary  will  send  a  representative 
who  will  give  instruction  in  its  use  and  the  system  of  paying  for 
milk  or  cream  on  the  basis  of  butter  fat. 


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